At the present time, solar cells are primarily silicon devices because of the maturity of the silicon processing art and the fact that silicon is one of the least expensive and most abundant materials available. Further, silicon based solar cells can be easily and inexpensively integrated into silicon circuits for collection and other functions. However, it is well known in the solar cell art that most silicon solar cells are able to convert only a small portion of solar energy into electricity. This is primarily due to the fact that the spectral range of Si photodiodes is confined to a wavelength range of between 200 nm and approximately 1100 nm.
In attempts too overcome the conversion drawbacks of silicon solar cells, some spectral conversion materials have been developed that absorb solar energy and reemit it in a different spectral range. Most of these spectral conversion materials provide “up-conversion” phenomena, which is the absorption of lower spectral range energy (or higher wavelength of light) and the reemission at a higher spectral range of energy (or a lower wavelength of light). Thus, up-conversion materials absorb spectral energy above 1100 nm (generally around 1500 nm) and reemit it at, for example, 980 nm. In current spectral conversion solutions, all of the up-conversion material is placed in proximity to the back surface of the solar cell. The use of a back reflector allows for the double pass of light (spectral energy) through the up-conversion layer.
One problem that occurs with this positioning of the up-conversion material is that because of the difference of the index of refraction between the silicon and the up-conversion material, the light reflected from the back reflector must impinge on the interface within a 60° angle of incidence. If the angle of incidence is less than 60° the light is simply reflected back into the up-conversion material and lost. Since the up-conversion material is assumed to emit light in a lambertian profile (i.e. in all directions), only ⅙ of the reemitted light is useable.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
An object of the present invention is to provide a new and improved solar cell with engineered spectral conversion.
Another object of the present invention is to provide a solar cell with engineered spectral conversion that is more efficient at converting solar energy.
Another object of the present invention is to provide a solar cell with engineered spectral conversion that is relatively easy to fabricate.
Another object of the present invention is to provide a new and improved method of fabricating solar cells with engineered spectral conversion.